Hello!
I was reading up on http://www.digitalmars.com/d/dll.html#com regarding
how to call DLLs with a COM interface, since this is exactly what I am
struggling with.
I'm trying to interface with proprietary DLLs that I know expose COM
interfaces. Fortunately, I have the documentation for them so I know
exactly what methods they expose.
There is, for example trtCom.dll, which exposes a trtComMgr class, which
has a method AboutBox(). I thought I'd start with calling that, since
it takes no arguments and returns nothing.
Now, it said in the article mentioned above that COM objects and D
interfaces are virtually the same thing, so I tried this:
extern(Windows)
{
interface MbtComMgr
{
void AboutBox();
}
}
But that wasn't very popular with the D compiler. It simply said:
Error: need 'this' to access member AboutBox
What would be the proper way of accessing a COM DLL?
The article said that "The sample code includes an example COM client
program and server DLL." What sample code is it talking about exactly? I
looked under C:\dmd\samples\d\mydll but found nothing that looks like an
example on this.
Cheers!
Henrik

But that wasn't very popular with the D compiler. It simply said:
Error: need 'this' to access member AboutBox

the interface is just an abstract type, you'll always need an object
that you access as such an interface. that object needs to be an
instance of some class that implements the interface.
usually the DLL would expose a C-style function that returns such an object.
for standard COM, the DLL exposes DllGetClassObject that returns a class
factory object, that can instantiate all COM objects contained in the
DLL. the class factory object (that implements IClassFactory) has a
CreateInstance method, that will give you object pointer for a requested
interface.
for more details, [1] is a good place to start. i also recommend the
book Essential COM by Don Box.

The article said that "The sample code includes an example COM client
program and server DLL." What sample code is it talking about exactly? I
looked under C:\dmd\samples\d\mydll but found nothing that looks like an
example on this.

you can look at my code for "seatd for scite" at [2], that plugs code
navigation functionality into the scite editor using com objects. the
relevant code is in src/scite/seatd_scite.dll and src/scite/scite_ext.d
i'm not following COM completely here, i.e. i'm not implementing
IClassFactory and the method that returns the object is not called
DllGetClassObject, but it's basically COM and it covers your problem as
well.
[1] http://en.wikipedia.org/wiki/Component_object_model
[2] http://seatd.mainia.de/

Hello!
I was reading up on http://www.digitalmars.com/d/dll.html#com regarding
how to call DLLs with a COM interface, since this is exactly what I am
struggling with.
I'm trying to interface with proprietary DLLs that I know expose COM
interfaces. Fortunately, I have the documentation for them so I know
exactly what methods they expose.
There is, for example trtCom.dll, which exposes a trtComMgr class, which
has a method AboutBox(). I thought I'd start with calling that, since it
takes no arguments and returns nothing.
Now, it said in the article mentioned above that COM objects and D
interfaces are virtually the same thing, so I tried this:
extern(Windows)
{
interface MbtComMgr
{
void AboutBox();
}
}
But that wasn't very popular with the D compiler. It simply said:
Error: need 'this' to access member AboutBox
What would be the proper way of accessing a COM DLL?

COM interfaces have to inherit from IUnknown. IUnknown is "magic" and the
compiler treats it specially.
Furthermore, I think you should put the extern(Windows) on the inside of the
interface, as I don't think putting it on the outside will affect the
calling conventions of the things on the inside. (Putting it on the outside
won't do much of anything, actually, except maybe change the name mangling
of the interface.)
So you'll have:
import std.c.windows.com;
interface MbtComMgr : IUnknown
{
extern(Windows):
void AboutBox();
}
:)

Hello!
I was reading up on http://www.digitalmars.com/d/dll.html#com regarding
how to call DLLs with a COM interface, since this is exactly what I am
struggling with.
I'm trying to interface with proprietary DLLs that I know expose COM
interfaces. Fortunately, I have the documentation for them so I know
exactly what methods they expose.
There is, for example trtCom.dll, which exposes a trtComMgr class, which
has a method AboutBox(). I thought I'd start with calling that, since
it takes no arguments and returns nothing.
Now, it said in the article mentioned above that COM objects and D
interfaces are virtually the same thing, so I tried this:
extern(Windows)
{
interface MbtComMgr
{
void AboutBox();
}
}
But that wasn't very popular with the D compiler. It simply said:
Error: need 'this' to access member AboutBox
What would be the proper way of accessing a COM DLL?
The article said that "The sample code includes an example COM client
program and server DLL." What sample code is it talking about exactly? I
looked under C:\dmd\samples\d\mydll but found nothing that looks like an
example on this.
Cheers!
Henrik

interfaces. Fortunately, I have the documentation for them so I know =

exactly what methods they expose.
There is, for example trtCom.dll, which exposes a trtComMgr class, whi=

ch =

has a method AboutBox(). I thought I'd start with calling that, sinc=

e =

it takes no arguments and returns nothing.
Now, it said in the article mentioned above that COM objects and D =

interfaces are virtually the same thing, so I tried this:
extern(Windows)
{
interface MbtComMgr
{
void AboutBox();
}
}
But that wasn't very popular with the D compiler. It simply said:
Error: need 'this' to access member AboutBox
What would be the proper way of accessing a COM DLL?

An interface on its own is just a contract saying how the actual instanc=
e =
will be layed out in memory and how it will be called (usually extern =
(Windows) for COM). You need an actual instance, which you can get from =
=
Windows with the CoCreateInstance call:
extern (Windows) IFooBar : IUnknown
{
...
}
CoInitialize(null); // initialize COM before getting the =
instance
scope (exit) CoUninitialize(); // close COM after we're finished
IFooBar instance; // this just declares a reference to the interface =
IFooBar which is null at first
CLSID clsid =3D ...; // you need to know the DLL's class id first!
CLSCTX clsctx =3D ...; // the context, normally CLSCTX_INPROC_SERVER
auto rc =3D CoCreateInstance(clsid, null, clsctx, clsid, =
cast(void**)&instance);
if (rc !=3D S_OK) throw new Exception("Couldn't create instance!");
/* now you can call the IFooBar instance */
instance.Release(); // release the instance
The important part is to get the instance pointer from COM with =
CoCreateInstance. It creates the instance and stores the pointer to it i=
n =
instance (that's why there's a cast(void**) in there). Deriving from =
IUnknown is important too 'cause then the housekeeping is done =
automatically and you just use the instance as if you'd created it with =
=
new. Don't forget to release the instance after you're done with it, don=
't =
delete it!
The definitions for CLSID etc. are in phobos and Tango, just search for =
=
them. If it doesn't work (like it did for me) I can recommend downloadin=
g =
the schooner project from dsource.org and using its win32 files - they =
have every definition and they work.
-Mike
-- =
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